In response to need for performance enhancement of mobile devices, hybrid vehicles, electric vehicles and the like, an increase of energy density and an improvement of charge and discharge characteristics have been required for lithium secondary batteries (lithium secondary batteries). In recent years, it has been considered that fibrous carbon such as a carbon nanotube having excellent electron conductivity, thermal conductivity and mechanical strength characteristics is used as an electrode material of the lithium secondary battery in order to further improve performance of the lithium secondary battery.
For example, Patent Literature 1 describes that, for the purpose of increasing discharge capacity, improving cycle characteristics and the like, a multilayer carbon nanotube as a conductive material synthesized by a vapor phase method is mixed with a positive electrode active material, this mixture is dispersed in a solvent (water or an organic solvent) obtained by dissolving a dispersant such as CMC (carboxylmethylcellulose) to prepare a slurry solution, and the prepared slurry solution is applied on a positive electrode collector.
Further, Patent Literature 2 describes that, in order to enhance handling property of a carbon nanotube which is a fibrous material having a large aspect ratio and improve conductivity as a conductive auxiliary agent for an electrode of a lithium secondary battery, orientation of the carbon nanotube, the content of Ca and the like are adjusted.
Further, Patent Literature 3 describes that, in order that fine carbon fibers such as carbon nanotubes, which are existing in an aggregate state, can be used as a battery electrode material, a mixture of an aggregate of the carbon fibers and solid particles whose sizes are limited is kneaded with a shear force applied to the mixture, and thus the particles covered with the fine carbon fibers can be obtained.